1. Field of the Invention
The present invention relates to fire extinguishing apparatus and more particularly to an electrical circuit for actuating fire extinguishing devices such as sprinkler heads.
2. Description of the Prior Art
One way of actuating a sprinkler head is for each head to be provided with an electrically actuable single shot actuator which is used to rupture a seal, for example the quartz bulb, of a sprinkler head to cause water or other fire extinguishing fluid to be discharged from the head. One such actuator is sold under the trade name Metron by Nobel's Explosives Company Limited of Ayshire, Scotland. Individually, these actuators operate satisfactorily but when used in large numbers and especially when it is desired to actuate a plurality of such actuators using a single trigger signal problems can arise due to the fact that when actuated the actuators can end up either in open circuit or a short circuit state in a random manner. This means that it is possible that only some of the desired number of actuators will actually be actuated which could have disasterous consequences.
In order to ensure that each actuator of a plurality of actuators is operated, one could wire the actuators in parallel but this is an expensive operation and causes difficulties in providing a trigger signal which will meet the manufacturer's specification for a drive signal which is for example, a current of 2 amps with a rise time of 100 microsecs.
Wiring the actuators in series would avoid the problems of cost and drive signal specification but does not itself solve the problem that some actuators may be in an open circuit mode after actuation and before the drive signal current can actuate any further actuators.